1. Technical Field
The present invention relates to a support apparatus for an insulator arm for a compact pylon.
2. Background Art
Polymer insulator arms are known to have been used to make pylons simpler, lighter and smaller. There also have been efforts to minimize the longitudinal distance between electric cables and holding the electric cables stably on the transmission pylons, which are metal structures used for supporting the transmission lines, while making the pylons smaller.
FIG. 1 shows a conventional insulator arm.
Referring to FIG. 1, the conventional insulator arm is constituted with a pair of primary insulator arms 10 and a pair of supplementary insulator arms 11. The primary insulator arms are installed on a main body of a pylon to support transmission line, and their supporting forces are reinforced by the supplementary insulator arms 11, which correspond, respectively, to the primary insulator arms 10 and are connected to the main body of the pylon.
For application in compact pylons, the conventional insulator arm is made of fiberglass reinforced plastics (FRP). The FRP is lighter than porcelain materials or glass materials and thus can be readily transported and installed. Moreover, the FRP has better leakage current characteristics and is more price-competitive than the porcelain materials. The insulator arm using the FRP can make the pylon lighter and smaller, thereby making it possible to reduce the land required for constructing the transmission pylons.
However, the FRP has an anisotropic structure, hence better tensile strength than the porcelain insulator, but the compressive strength is only between ⅕ and 1/10 of that of the porcelain insulator. Accordingly, in the case that a torsional stress, which can occur in a transmission line, is applied to the insulator arm made of the FRP by the wind, adhesive force is lost in resin that organically binds glass fibers within the FRP, causing internal cracks and possibly resulting in deterioration due to permeation of moisture. Besides, if the temperature and humidity are increased, the mechanical strength of the insulator arm can be critically sacrificed.